To increase productivity, agricultural vehicles, such as combines, are becoming larger, headers are becoming wider, and travel speeds are increasing during harvest. Additionally, harvesting operations in a large field often involve simultaneous harvesting and unloading of harvested crop material. Typically, the combine has an unloading system including an unloading tube containing a helical auger, that is deployed for unloading crop material from an on board grain tank into an accompanying receiving container, such as a tractor pulled cart, wagon, truck, trailer, or the like. However, this manner of unloading has been found to be slower than desired for many agricultural operations. Also, as a consequence of necessary spacing between the auger flight edges and the interior surface of the unloading tube, the crop material can be damaged therebetween.
Belt conveyors have found to be an advantageous alternative to auger type conveyors for several reasons. For instance, the belts are lighter, less costly, and may be operated at faster speeds than augers and thus have higher potential capacity. Belt conveyors can also deliver the crop material in a more continuous manner with less vibration. In general, it has been found that conveying crop material using belts results in less crop damage than augers.
As a result, for some agricultural applications, it is desired to replace auger conveyors with belt conveyors. Particularly for unloading conveyors of agricultural harvesters, wherein the unloading often occurs while the harvester is moving, including over uneven terrain and while on slopes and hills, under windy and other adverse weather conditions, it is desired to utilize covered conveyors, such as belt in tube conveyors. In a belt in tube conveyor, the belt runs through an elongate tube, typically having a lower peripheral portion of round or curved sectional shape, and the belt conforms to the lower periphery of the tube, so that an upwardly concave, typically curved shape, is imparted to the belt, particularly an upwardly facing material carrying feed surface thereof. The belt then typically returns externally along the underside of the tube. Generally, the ends of the belt encircle cylindrical rollers, such that the ends of the belt adjacent and about the rollers are flat and wider than a sideward extent or diameter of the unloading tube. Before or as the belt enters the tube, it is gradually transitioned in some manner from the flat shape to conform to the concave, e.g., curved or rounded, shape of the lower portion of the tube.
In use, belt in tube conveyors are typically fed from a hopper, bin or other container, and the only force acting on the material is gravity, so that the material is only propelled downwardly, although it may fan out or be directed laterally by a spout or chute. The downwardly flowing material can be accelerated by gravity to a significant downward velocity, and is typically deposited on a belt moving horizontally or at an upward incline, so both the direction of movement of the material will have to be changed, possibly significantly (e.g., from directly downward to an upward incline), and energy imparted to the material by its downward movement will have to be dissipated and/or redirected in some manner. The material is typically deposited onto the flat region of the belt or partially onto the transition region outside of the tube where the belt is formed into the concave shape. As the belt is transitioned to the concave shape while carrying material, some of the material will be lifted and shifted laterally toward the center of the belt, possibly while additional material is deposited onto it, such that turbulence can occur that will impede movement and acceleration of the material to the belt speed, which can decrease the effective capacity of the conveyor and conveying speed.
It has also been observed that the belt's fill level is reduced as the speed of the belt increases and the incline of the conveyor increases. For example, some known commercially available portable belt conveyors operate at belt speeds of about 600 feet per minute, and at inclines of 15 to 30 degrees. These are within the anticipated ranges of speeds and inclines desired for unloading application for agricultural vehicles, particularly harvesters. Experience with these conveyors in conveying common grains is that the belt is less than full at these conditions, with a general rule that the fill decreases as the incline increases, largely for the reasons just explained. As a result, use of belt in tube conveyors for unloading applications has been found to suffer from shortcomings in terms of speed and/or capacity.
Thus, what is sought is a manner of increasing the fill of a belt in tube conveyor system for agricultural products to take advantage of the potential speed of operation and other benefits thereof, particularly for use as an unloading conveyor for a machine or vehicle such as a harvester, and which overcomes one or more of the shortcomings and limitations, set forth above.